Electric arc torch



Q, 1 Z 'StAhCH ROOM April 23, 1964 J. A. BROWNING 3,

\ ELECTRIC ARC TORCH File d Aug. 7. 1961 INVENTOR. I

"WWWW United States Patent 3,131,288 ELECTRIC ARC TORCH James A.Browning, Hanover, N.H., assignor to Thermal Dynamics Corporation, acorporation of New Hampshire Filed Aug. 7, 1961, Ser. No. 129,750 1Claim. (Cl. 219-121) My invention relates to electric arc torches andrelates more particularly to a torch in which a plasma forming gaseouselement may be introduced to stabilize and be heated by a high-pressureelectric arc. Such torches are well exemplified by the device shown inUS. Patent No. 2,960,594, issued to Merle L. Thorpe.

In accordance with my invention, I propose to add to the conventionalgaseous elements a liquid such as water. The resulting dual mixture ispreferably introduced into a flow passage through which an electric arcis established. If this is done in such a way as to create a strongvortex, the heavier liquid particles will form a film on the insidewalls of the arc passageway for purposes hereinafter explained.

It is, therefore, a principal object of my invention to provide improvedmeans for operating arc torches using both liquid and gaseous elements.

It is a further object of my invention to employ the methods thereofwith minimum modifications of known devices, thereby realizing theadvantages at minimum expense.

For a better understanding of the invention reference is now made to thefollowing detailed description and the accompanying drawing, in whichFIGURE 1 is a torch of simplified design, in longitudinal cross section;and

FIGURE 2 is a plan view of a swirl ring element used in the torch ofFIGURE 1.

Referring now more particularly to FIGURE 1, a torch body 11 is showncontaining an electrode 12, a swirl ring 13 and a nozzle 14. These lastthree elements are held securely by means of a nut 15 threaded on to theend of the torch body 11. A tube 19 is used to supply a mixture ofplasma forming gas and water (both under suitable pressure) through aslot 21 and thence into annular chamber 22 surrounding the electrode 12.The mixture travels through tangential slots in swirl ring 13, bestshown in FIGURE 2, and enters the arc passage in the nozzle 14 in theform of a strong vortex.

An electric arc is provided by supplying the torch with a source ofcurrent, not shown, through lead 27, to the electrode 12. The electricalcircuit is completed by the arc itself, shown at 17, the Work 25, andlead 26 connected to the source. It will be appreciated that the deviceis shown in the transferred mode of operation; that is, the Work acts asthe second electrode. If it is desired that the are be wholly containedin the torch itself, the nozzle 14 may serve as the second electrode inwhich case the lead 26 would be attached thereto. Both of these modes ofoperation are well known in the prior art, and this invention isapplicable in either case. In FIGURE 1, the device is shown beingemployed as a cutting torch applied to the work piece 25.

Before reaching the swirl ring 13, the liquid portion of the mixtureintroduced through tube 19 serves to provide a cooling film over thebody of electrode 12. After entering the passageway of the nozzle 14,the centrifugal 3,131,288 Patented Apr. 28, 1964 forces set up by theaction of the vortex drive the heavier liquid against the inner walls ofthe arc passageway. This film effectively cools and insulates thematerial of the nozzle from the heat of the are 17. The arc creates aplasma stream with the lighter gaseous element which remains nearer thecenter of the vortex. Since the cooling medium is on the interiorsurfaces of the nozzle pas sage it is possible to use materials of lowthermal conductivity for nozzle pieces, such as ceramics.

The rapidly rotating film of cooling liquid passes downward (as seen onFIGURE 1) and emerges from the torch in a diverging spray cone 18. Theshape of this cone may be controlled by vortex intensity, nozzle length,and nozzle exit configuration. I have found that the amount ofdivergence is important in many practical applications, since wateremerging too close to the zone of operation may interfere with theheating (and in the case shown) and cutting action. However, it issometimes desirable to provide a divergence just wide enough to avoidthe desired heated zone, yet close enough to aid in cooling the workpiece in the areas not to be heated. For example, in cutting thin metalplates the warpage of the sheet may be greatly reduced by supplying thecooling medium to the area immediately adjacent to the cut.

I have also found it desirable in some instances to suspend smallparticles of an opaque substance in the liquid supplied to the torch.Fine particles of silicon carbide, for example, further aid coolingaction by markedly reducing radiation through the film. In addition, theintense glare of the arc extending from the torch is attenuated by theresulting cone of opaque particles and liquid.

The liquid provides a practical vehicle for opaque particles and I havefound that the liquid film has much greater ability to constrict andthereby control the arc column than the use of a compressible gas alone.While this desirable action is not completely understood, I theorizethat ionization levels in the annular region around the are are kept lowand the arc is kept constricted much more effectively. Thus highercurrent densities with torches no larger than prior art devices areeasily achieved.

While I have described a particular embodiment of my invention forillustrative purposes, modifications within the spirit and scope of theappended claims hereto may occur to persons skilled in this art. Forexample, instead of solid particles in suspension, a dye may be added tothe liquid to increase its opacity. This is most effective in achievingthe desired results.

I claim:

The method of operating an electric arc torch of the type described, inwhich one or more plasma forming gaseous elements are supplied underpressure to said torch, comprising mixing a liquid with said gaseouselements, and introducing the resulting mixture under pressuretangentially into the arc passageway of said torch to form a vortexdriving the liquid portion of said mixture against the inner walls ofsaid passageway.

References Cited in the file of this patent UNITED STATES PATENTS1,935,593 Wist Mar. 14, 1933 1,963,729 Alexay June 19, 1934 2,768,278Gaines Oct. 23, 1956 2,768,279 Rava Oct. 23, 1956 2,906,858 Morton Sept.29, 1959

